Interstitial lung disorders represent 15 to 20 percent of all diseases of the alveolar structures; in most cases these disorders cause significant disability and many are fatal. Studies of the natural history, etiology, pathogenesis and therapy of these disorders have made major inroads in the understanding of these diseases. Most importantly, is the development of the concept of the inflammatory and immune effector cells are critical determinants in the pathogenic process. Evaluation of the alveolitis of these patients has led to significant insights into the processes by which the alveolar structures are injured and repaired. As part of these studies insights have been gained into the role of the alveolar macrophage, T-lymphocyte, neutrophil, and eosinophils as well as how fibroblasts are recruited, anchored and simulated to replicate.